1. Field of the Invention
The present invention relates generally to mirroring technology in storage systems.
2. Description of Related Art
Volume mirroring is the replication of a first (primary) logical volume to a separate mirror (secondary) logical volume. As updates are made to the primary volume, the updates are also made (mirrored) to the mirror volume. Thus, the mirror volume is a complete and separate copy of the primary volume. Volume mirroring technology may be used to enable recovery of data upon the occurrence of data loss in the primary volume. Depending on the technologies used and the desired level of data protection, mirroring can be performed synchronously, asynchronously, semi-synchronously, or point-in-time, and the mirror volume may be a local volume in the same storage system as the primary volume, or may be a remote volume located in a separate or remote storage system.
Current volume mirroring technology requires that the mirror volume have a size equal to or greater than the size of the primary volume being mirrored, regardless of the actual data content on the primary volume. However, in many cases a primary volume may contain a large amount of duplicated or redundant data, such as backups of files, different versions of files, and the like, that are related to original files also stored on the primary volume. Accordingly, it would be advantageous to reduce the amount of redundant or secondary data created or copied by mirroring technology, and thereby reduce the size of the mirror volumes and the overall storage capacity required to accommodate mirroring operations.
U.S. Pat. No. 7,065,619, to Zhu et al., filed Dec. 20, 2002, the disclosure of which is incorporated herein by reference, is directed to a data storage system that determines whether a data segment has been stored previously using a summary stored in a low latency memory. However, the prior art is not able to be applied to de-duplication of data in a mirror volume that forms part of mirrored pair with a primary volume which has exactly the same volume size on physical disk.